Collapsible acetabular reamer

ABSTRACT

A method and apparatus for performing minimally invasive hip surgery to implant an acetabular shell into the acetabulum. A collapsible acetabular reamer is moveable between an expanded position and a collapsed position. In the expanded position, the reamer reams the acetabulum. In the collapsed position, the reamer can fit through a small minimally invasive incision.

FIELD OF THE INVENTION

The disclosure herein generally relates to a method and apparatus forperforming minimally invasive hip replacement surgery for the acetabulumusing a collapsible acetabular reamer.

BACKGROUND OF THE INVENTION

Traditional hip replacement surgery has been used in the United Statessince as early as the 1960's. The surgical technique to implant a hiphas not drastically changed over the years, and today, this technique isquite successful. In fact, the surgical technique is prolifically usedthroughout the world and has a known success rate of over 90%.Certainly, the traditional surgical technique is fundamentally sound andpredictable.

Unfortunately, traditional techniques to implant a hip have wellrecognized shortcomings. Most importantly, a rather large incision ismade on the side of the hip. The incision can extend from 6 to 12inches; the actual length of the incision depends on the size of thepatient and type of surgery (revision versus total hip arthroplasty, forexample). A long, deep incision can divide a number of importantstabilizing muscles and tendons and further damage the hip joint andsurrounding soft tissue. Inevitably, long incisions lead to larger bloodlosses, longer rehabilitation times for patients, and unsightly scarlines. A patient can easily spend four or five days in the hospitalafter a total hip arthroplasty, for example.

Recently, surgeons have been developing new, less invasive surgicaltechniques to perform total hip arthroplasty and revision hip surgery.Minimally invasive surgery, or MIS, is one such technique with greatpromise to become a popular and accepted technique for implanting a hip.

MIS has significant advantages over traditional hip replacement surgery.Most importantly, a rather small incision is made on the side on thehip. This incision is approximately 3 to 5 inches long, and the benefitsof a shorter incision are enormous.

First and foremost, the patient can recover in a much shorter period oftime after a MIS. The recuperation time in the hospital can be a fewdays and significantly reduce the cost to both the patient and hospital.In fact, some patients are leaving the hospital within 24 to 48 hoursafter the surgery. Obviously, this shortened time period is extremelyimportant to the patient.

As another advantage, MIS is less invasive and traumatic to the patient.Significantly less soft tissue is disrupted in a minimally invasivesurgery compared to a traditional hip surgery. Also, the amount of bloodloss is reduced, and patients will require fewer blood transfusions.Further, the length of the scar is significantly smaller, and thesescars are more cosmetically appealing. The incisions themselves heal ina much shorter period of time and are much less painful than a long tenor twelve inch incision. As such, the patient can sooner return to workor enjoy recreational activities. In short, the patient can more quicklyreturn to a normal way of life.

Presently, instruments to perform MIS are being developed and refined.These instruments have a vital role in the ability to perform asuccessful minimally invasive surgery. As one important consideration,these instruments must be able to fit through the small MIS incision.Traditional acetabular reamers are typically hemispherical and haverelatively large diameters with deep shell heights. These reamers do notfit well through the small MIS incision.

In short, instruments, and in particular acetabular reamers, play avital role in MIS surgery for hip implantation. It therefore would beadvantageous to provide a new acetabular reamer and method of use forperforming a minimally invasive surgery to implant a prosthetic hip.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forperforming minimally invasive hip surgery for the acetabulum using acollapsible acetabular reamer. The collapsible acetabulum reamer of thepresent invention generally comprises a body having two cuttingsurfaces. Each cutting surface has a semicircular cutting section and abridge or mounting section. The cutting surfaces rotate about a commonaxis and have longitudinal axes that are concentric. The mountingsections extend between the ends of the cutting surfaces and are adaptedto connect to a tool driver. Most importantly, the body of the reamer ismoveable between two different and distinct positions, a collapsedposition and an expanded position. In the expanded position, the bodyforms a hemispherical shape and the two cutting surfaces are lockedtogether. A tool driver can be attached to the mounting section, and thereamer used to ream the acetabulum. In the collapsed position, thecutting surfaces are unlocked and moved or retracted together. Here, thebody no longer forms a hemispherical shape but has more a semi-circularshape. In the collapsed position, the reamer is much smaller and, thus,can more easily fit through a small MIS incision.

Thus, the reamer can physically change its shape back and forth betweenan expanded position with the body adapted to ream the acetabulum and acollapsed position with the body adapted to pass through a small MISincision. The movement of the reamer between two different and distinctpositions provides numerous advantages over traditional reamers thatcannot change shape and size.

The method of the present invention generally comprises the steps oftemplating the acetabulum to estimate the size of reamer and acetabularcomponents; incising the surgical site with a single incisionapproximately three inches in length; exposing the acetabular joint anddislocating the hip from the acetabulum; providing a collapsibleacetabular reamer; retracting the acetabular reamer to its collapsedposition; positioning the reamer through the incision while in thecollapsed position; expanding the reamer to its expanded position;reaming the acetabulum with the expanded reamer; retracting the reamerback to its collapsed position; removing the reamer from the incisionwhile in the collapsed position; inserting and aligning an acetabularshell into the reamed acetabulum and impacting the shell into place;inserting and impacting an insert into the shell; and closing thesurgical site.

One important advantage of the present invention is that the method andacetabular reamer are used in a minimally invasive orthopedic hipsurgery. A single, small three inch incision is made at the surgicalsite on the side on the hip. The method of the present invention, thus,enjoys the benefits of a shorter incision compared to traditional hipsurgery that uses a much longer incision. As one benefit, the patientcan recover in a much shorter period of time after a MIS. Therecuperation time in the hospital can be a few days and significantlyreduce the cost to both the patient and hospital. This shortened timeperiod is extremely important to the patient. Further, MIS is lessinvasive and traumatic to the patient. Significantly less soft tissue isdisrupted in a minimally invasive surgery compared to a traditional hipsurgery. Also, the amount of blood loss is reduced, and patients willrequire fewer blood transfusions. Further, the length of the scar issignificantly smaller, and these scars are more cosmetically appealing.The incisions themselves heal in a much shorter period of time and aremuch less painful than a long ten or twelve inch incision. As such, thepatient can sooner return to work or enjoy recreational activities. Inshort, the patient can more quickly return to a normal way of life.

Another important advantage of the present invention is that acollapsible acetabular reamer is used. This reamer is specificallydesigned and adapted to be used in minimally invasive surgicaltechniques for reaming the natural acetabulum of a patient.Specifically, the reamer is moveable back and forth between thecollapsed and expanded position. In the expanded position, the reamerhas a generally hemispherical shape that is adapted to ream theacetabulum. In the collapsed position, the reamer is much smaller. Here,it has a more semicircular shape. In the collapsed position, the reamercan more easily fit through a small MIS incision.

As another important advantage, since the reamer is readily changeablefrom the expanded position to the collapsed position, the body orcutting section will not damage or disrupt the sides of the woundchannel or surgical site. In the collapsed position, the body of thereamer can easily fit through a small 3–5 inch MIS incision. As such,the body will not disrupt or harm the sides of the incision as thereamer is being placed through the surgical site.

As another advantage, the reamer has a limited number of parts. As such,it can consistently and reliably move between the expanded and collapsedpositions. Further, the reamer is not expensive to manufacture.

Further yet, the collapsible reamer is easy to use and facilitates theMIS implantation procedure. As such, the acetabular reamer can appeal toa wide range of orthopedic surgeons with various skills and experience.Further yet, the training and skill level required to use the reamer andbecome proficient with it is not overly taxing on the orthopedicsurgeon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a collapsible acetabular reamer in anexpanded position according to the invention.

FIG. 2 is a perspective view of the first cutting surface of thecollapsible acetabular reamer.

FIG. 3 is a perspective view of the second cutting surface of thecollapsible acetabular reamer.

FIG. 4 is a perspective view of the collapsible acetabular reamer in acollapsed position.

FIG. 5 is a perspective view of an alternate embodiment of thecollapsible acetabular reamer in an expanded position.

FIG. 6 is a bottom perspective view of the reamer of FIG. 5.

FIG. 7 is a bottom view of the reamer of FIG. 5 in a collapsed position.

DETAILED DESCRIPTION

The instruments, method, and steps of the present invention are nowdescribed in more detail. The method describes the steps to perform aminimally invasive surgery to implant a prosthetic acetabular componentinto the natural acetabulum of a patient. Some of these steps describedin the method are known to those skilled in the art and will not bediscussed in great detail. Further, one skilled in the art willappreciate that certain steps may be altered or omitted while othersteps may be added without departing from the scope of the invention.The novel steps of the present invention, for example, can be applied tototal hip arthroplasty, to revision surgeries for total and partial hipreplacement, and to other orthopedic surgeries using minimally invasivesurgical techniques.

To facilitate a discussion of the present invention, the method ofimplanting a prosthetic acetabular component is divided into a pluralityof steps or sections. Each of these sections is discussed seriatim. Morespecifically, the method of the present invention teaches how to implanta prosthetic acetabular shell and insert into the natural acetabulumusing a collapsible acetabular reamer to ream the acetabulum through asmall MIS incision. For illustrative purposes, the discussion focuses onimplanting a Converge™ Acetabular System of Centerpulse Orthopedics Inc.of Austin, Tex. This system illustrates one possible acetabular systemthat can be used. One skilled in the art will appreciate that other,different acetabular systems can also be used with the method andapparatus of the present invention without departing from the scope ofthe invention.

Templating the Acetabulum

Typically, the side of the acetabulum to be reconstructed is templated.Use of a template enables the surgeon to make an estimation of the sizeof reamers to be used and the size of acetabular component to beinserted. The acetabulum is templated on the both the anterior-posterior(A/P) and lateral radiographs. The hemisphere of the acetabularcomponent is aligned with the mouth of the bony, natural acetabulumwhile simultaneously avoiding any osteophytes. On the A/P radiograph,the acetabular component should rest on the floor of the cotyloid notchand may touch the illoischial line. Further, the component should have amaximum lateral opening of about 40°. On the groin lateral radiograph,the cup size selected should contact the anterior and posterior rim ofthe bony, natural acetabulum and the medial subchondral bone. A correctposition of the acetabular component will anatomically reproduce thecenter of rotation of the femoral head. If a bony defect is identified,use the correctly placed template to measure for proper size of theacetabular component and determine any need for bone graft.

Incising the Surgical Site

A relatively small, single minimally invasive incision is made at thesurgical site. A minimally invasive incision for this procedure has alength from about 2½ inches to about 4 or 5 inches. The incision isslightly curved or straight, commences near the vastus tubercle, andcontinues toward the greater trochanter and posterior inferior spine.The incision should be carried down through subcutaneous tissue andfascia lata. Any muscle tissue should be gently split in line with itsfibers. Retractors can now be used, as preferred, to retract portions ofthe site. At this time, a leg length measurement can be taken usingtechniques known in the art.

Exposing the Acetabular Joint and Dislocating the Hip From theAcetabulum

Next, the knee is flexed, and the leg is internally rotated. Using a hotknife, the piriformis, short external rotators, quadratus femoris, andsome posterior capsule are incised off the posterior trochanter toexpose the lesser trochanter. Dislocation of the hip can now occur. Abone hook or skid may be used to avoid excess torsion on the femoralshaft.

At this time, retractors may be placed, for example under the femoralhead or lesser trochanter, in order to achieve visualization for propertransection of the femoral neck if this procedure is desired at thistime. If such transection occurs, the femoral neck should be transectedat the templated level. Then retract the femur in an anterior directionto expose the acetabulum. Care should be taken to protect the sciaticnerve.

A retractor can be placed on the pelvis to hold the femur in an anteriorposition to the acetabulum. The capsule can be retracted in theposterior using retractors or pins. After the labrum and osteophytes areremoved, at least a partial view of the acetabulum should be available.

Providing A Collapsible Acetabular Reamer

A collapsible acetabular reamer is provided to ream the naturalacetabulum. The reamer is designed and adapted to be used with minimallyinvasive surgical techniques of the acetabulum. Specifically, the reameris moveable between an expanded position and a collapsed position. Thereamer is more fully discussed in connection with the figures.

Collapsing the Acetabular Reamer

In order to fit easily through the MIS incision, the reamer is retractedto its collapsed position. Specifically, the two cutting surfaces aremoved or collapsed toward each other. The body of the reamer, thus,transitions from a generally hemispherical shape to a more semicircularshape. The latter shape is much smaller in size and shape. Once thereamer is collapsed to its smaller size, it is placed through the smallMIS incision.

Expanding the Acetabuler Reamer

Once the collapsed reamer is positioned through the incision and intothe surgical site, the reamer is expanded. Specifically, the two cuttingsurfaces are moved or spread apart away from each other and then lockedtogether. The body of the reamer, thus, transitions from a generallysemicircular shape back to a hemispherical shape. The reamer is nowshaped to ream the acetabulum. Before reaming occurs, the reamer isattached to a tool driver.

Reaming the Acetabulum

Reaming of the acetabulum should begin with a reamer that is two sizessmaller than the preoperatively selected acetabular component size. Asmaller reamer ensures that the fit does not exceed theanterior-posterior diameter. Of course, the reamer should not be sosmall that excessive anterior or posterior reaming occurs. The reamersof the present invention can be made with various sizes to accommodatereaming of the acetabulum.

After an appropriately sized reamer is connected to the driving tool,reaming should begin transversely toward the cotyloid notch. The ridgesof the horseshoe (or medial osteophytes) should be removed. Reaming thencontinues in the position of desired anteversion while simultaneouslycreating a hemisphere. Larger reamers are used until the anterior andposterior rim of the acetabulum is contacted. The reamer should not besunk below the superior rim of the bony acetabulum or reamed through thecortical bone of the cotyloid notch. Cancellous bone will be evidentwhere the horseshoe ridges have been removed. The proper size trialshell should be selected according to the size of the reamer.

Collapsing the Acetabular Reamer

After reaming of the acetabulum is complete, the reamer is removed fromthe surgical site. In order to fit easily through the MIS incision, thereamer is retracted back to its collapsed position. Specifically, thetwo cutting surfaces are moved or collapsed toward each other. The bodyof the reamer, thus, transitions from a generally hemispherical shape toa more semicircular shape. Once the reamer is collapsed to its smallersize, it is removed through the small MIS incision and from the surgicalsite.

Providing An Acetabular Shell Impaction Instrument

An acetabular shell impaction instrument is provided to align and thenimpact the acetabular shell into the natural acetabulum. The instrumentis designed and adapted to be used with minimally invasive surgicaltechniques of the acetabulum. Specifically, the instrument has a curvedshape to fit through the small incision at the surgical site andprecisely impact the implanted shell at the correct angular orientation.Further, this curvature enables the instrument to engage the shell inthe acetabulum without disrupting the incision and surrounding softtissue. Further yet, the instrument is adapted to move and align theacetabular shell while it is positioned in the acetabulum. It isimportant to position properly the shell before it is impacted andpermanently seated in the acetabulum.

Inserting an Acetabular Shell Into the Acetabulum

Some acetabular shells may be provided with flared rims and outer boneengaging spikes. In order to insert such a shell, cancellous bone slurrymay be added within the acetabulum to fill existing bone cysts andprovide an interface layer. Addition of this slurry typically occurs intotal hip arthroplasty situations.

The distal connection end of the impaction instrument is engaged andconnected to the shell. The shell is partially inserted into theacetabulum until the rim begins to engage bone. The implant is thenpositioned with the instrument to the desired angular orientation, suchas abduction and anteversion. Preferably, the shell is positioned with20° to 25° of anteversion and with an abduction angle of about 35° to45°. The anteversion can be verified using techniques known to thoseskilled in the art. The proximal impaction end of the instrument is thenimpacted with a mallet or similar instrument. Force from the mallet istransferred from the instrument to the shell as it is driven andpermanently seated into the natural acetabulum. The shell should bedriven into the acetabulum until the outer fixation spikes centrallyengage into cancellous bone.

Removing and Installing Screw-Hole Plugs

The implant shell may be provided with screw-hole plugs, seals, or thelike. In this instance, after the shell is properly seated in theacetabulum, one or more of the plugs may be removed with an instrument.Further, the implant shell may be provided with screw-hole plugs or adome plug that may be installed or inserted into the shell. Typically,these plugs have a head with a tool engaging recess. A threaded shaftextends from the head and is adapted to threadably engage a threadedbore in the acetabular shell.

Drilling Holes and Installing Bone Screws

Next, a drill bit is provided, connected to a flexible driver, andpositioned into a selected screw hole. As the hole or bore is drilled,care should be taken to protect the sciatic nerve and superior glutealartery. A depth gauge may be inserted into the drilled holes todetermine the depth for a corresponding bone screw. If desired, atapping bit may be connected to the driver to tap the hole.

A bone screw is then positioned into the surgical site so the threadedshaft on the bone screw passes through the screw-hole opening in theacetabular shell and into a drilled hole. The bone screw should beseated into the countersunk holes of the shell so the acetabular insertcan properly snap into the shell.

Inserting and Impacting an Insert Into the Shell

Various inserts known to those skilled in the art (such as standard,hooded, and protrusion inserts) can be inserted into the implant shell.Once the appropriate size and style insert is selected, the insert isconnected to an instrument. The insert is positioned into the cavity ofthe shell and should be rotated to align with the antirotational pegs onthe shell. A surgical mallet is used to strike the proximal end of theinstrument to seat the insert into the shell.

Closing Surgical Site

Once the insert is firmly connected to the shell, all instruments anddevices are removed from the site. The acetabular shell and insertshould now be properly positioned. Closure of the site may occur withwell known techniques, such as posterior and anterior lateralapproaches. Further, this disclosure will not discuss post-operativeprotocol or rehabilitation as such procedures are known in the art andtailored to meet the specific needs of the patient.

Detailed Description of Acetabular Reamer

One important advantage of the present invention is that collapsibleacetabular reamer is used. This reamer is specifically designed andadapted to be used in minimally invasive surgical techniques for reamingthe natural acetabulum of a patient.

Looking to FIGS. 1–3, the acetabular reamer 10 has a body 12 thatincludes a first cutting surface 14 and a second cutting surface 16. Thefirst cutting surface 14 includes a semicircular cutting section 20 withedges 21 that are adapted to cut or ream bone, such as the acetabulum ofa patient. Cutting section 20 terminates in two ends 22 a and 22 b.These ends connect to a bridge or mounting section 24. Mounting section24 has two straight, rectangular base sections 26 a and 26 b and acentrally located circular hub 28. A capture 30 is formed at the top ofthe cutting section 20 as a rectangular or square recess. Threerectangular or square surfaces 32 a, 32 b, and 32 c define the recessand capture. An elongated cylindrical post 36 extends between thecapture 30 and hub 28. This post has a cylindrical bore 38 with oneopening 40 formed through surface 32 b in capture 30 and another opening42 formed through the center of hub 28.

The second cutting surface 16 includes a semicircular cutting section 50with edges 51 that are adapted to cut or ream bone, such as theacetabulum of a patient. Cutting section 50 terminates in two ends 52 aand 52 b. These ends connect to a bridge or mounting section 54.Mounting section 54 has two straight, rectangular base sections 56 a and56 b and a centrally located circular hub 58. An elongated cylindricalrod 60 extends between a top 62 of cutting section 50 and a center ofhub 58. A biasing member 66 is disposed around the rod 60 adjacent thetop 62 of cutting section 50. This biasing member may have variousconfigurations known in the art, and is shown as a coiled spring.

When the first and second cutting surfaces are connected, rod 60 ispositioned through bore 38. As such, both cutting surfaces are able torotate about a common longitudinal or central axis 70.

One important advantage of the present invention is that the body 12 ofthe acetabular reamer 10 is moveable between two different and distinctpositions. FIG. 1 shows the first position wherein the body is in anexpanded or enlarged state. Here, the first cutting surface 14 and thesecond cutting surface 16 are perpendicular to each other. In thisposition, the body has a substantially hemispherical or dome shape.During use, the first cutting surface 14 moves axially or upwardly alonglongitudinal axis 70. Specifically, post 36 slides upwardly along rod60, and simultaneously biasing member 66 gets compressed between surface32 b and the underside of cutting surface 16 at top 62. As biasingmember 56 gets compressed, cutting surface 16 becomes engaged and lockedin capture 30. The cutting surfaces, in this position, are lockedtogether in a hemispherical, expanded shape.

When the cutting surfaces are locked together, the reamer can be used toream or cut bone. The mounting sections 24 and 54 can be adapted toengage and connect with a driving tool. These driving tools and variousconnections between the tool and the reamer are known in the art. U.S.Pat. No. 6,250,858 entitled “Tool Driver and Tools Thereof” and U.S.Pat. No. 5,658,290 entitled “Assembly Comprising Reamer Spindle andReamer for Surgery” teach such driving tools and connections. These twopatents are incorporated herein by reference.

FIG. 4 shows the second position wherein the body is in a collapsed orretracted position. Here, the first and second cutting surfaces aregenerally parallel with each other. In this position, the body has asubstantially semicircular shape. In other words, the hemispherical ordome shape has been significantly reduced in size and collapsed to asemicircular shape.

In order to move the reamer from the first position to the secondposition, the first cutting surface 14 moves axially downwardly alonglongitudinal axis 70. As post 36 slides down along rod 60, biasingmember 66 is uncompressed between surface 32 b and the underside ofcutting surface 16 at top 62. Capture 30, thus, disengages from cuttingsurface 16. The two cutting surfaces are unlocked and free to rotaterelative to each other about longitudinal axis 70. As such, the cuttingsurfaces can be rotated until they are substantially parallel with eachother. Stop members 80 a and 80 b may be provided on the ends 22 a and22 b, respectively, of cutting section 20 in order to prevent cuttingsurface 14 from spinning through cutting surface 16.

One important advantage of the present invention is that in thecollapsed position, the body of the reamer has a smaller size than inthe expanded position. Specifically, the body has been reduced from ahemispherical shape to a generally semicircular shape. The latter shapeis smaller and easier to fit through a small MIS incision. Thus, thereamer can physically change its shape back and forth between anexpanded position with the body adapted to ream the acetabulum and acollapsed position with the body adapted to pass through a small MISincision. The movement of the reamer between two different and distinctpositions provides numerous advantages over traditional reamers thatcannot change shape and size.

After reading this disclosure, one skilled in the art will appreciatethat the body of the reamer can be altered and still be within the scopeof the invention. Various embodiments can be used to create anacetabular reamer that is moveable between two positions in order tomore readily fit through small MIS incisions. FIGS. 5–7 show one suchembodiment.

FIGS. 5–7 show an acetabular reamer 100 that is similar to the reamer 10discussed in connection with FIGS. 1–4. As such, only significantdifferences between these two reamers will be discussed.

Reamer 100 has a body 112 that includes a first cutting surface 114 anda second cutting surface 116. These cutting are similar to the cuttingsurfaces 14 and 16. As one difference, cutting surface 114 includes amounting section 124 with two straight, rectangular base sections 126 a,126 b and a capture 130. The capture is formed as a rectangular orsquare recess and is defined with three surfaces, 132 a, 132 b, and 132c. Surface 132 b includes a central, circular hub 140. A cylindricalbore 142 extends through the hub 140. Another capture 150 is oppositelydisposed from capture 130. Capture 150 is formed along cutting section152 as a rectangular or square recess defined with three surfaces 154 a,154 b, and 154 c. Surface 154 b includes a bore 156 that aligns withbore 142.

Cutting surface 116 includes a rod 160 that extends between cuttingsection 162 and mounting section 164. This rod is positioned throughbores 142 and 156 to connect the first and second cutting surfaces.Further, one end of the rod 160 can include a twisted guide channel orcut 170. This cut rotationally guides or twists the first and secondcutting surfaces to and from the collapsed and expanded positions. Moreparticularly, FIGS. 5 and 6 show the body 112 in a hemispherical orexpanded position, and FIG. 7 shows the body in a substantiallysemicircular or collapsed position.

The acetabular reamers of the present invention have been shown in useto ream a natural acetabulum of a patient. One skilled in the art willappreciate that the reamers of the present invention can be utilized inother surgical indications as well. For example, the reamers can beadapted to be used to ream or cut bone for a MIS knee surgery, shouldersurgery, or other MIS surgeries that require a reamer.

It should be emphasized that although the method of the presentinvention was described with a specific number and sequence of steps,these steps can be altered or omitted while other steps may be addedwithout departing from the scope of the invention. As such, the specificsteps discussed in the preferred embodiment of the present inventionillustrate just one example of how to utilize the novel method and stepsof the present invention. Further, although illustrative embodiments andmethods have been shown and described, a wide range of modifications,changes, and substitutions is contemplated in the foregoing disclosureand in some instances, some features of the embodiments or steps of themethod may be employed without a corresponding use of other features orsteps. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theembodiments disclosed herein.

1. A method for using minimally invasive surgery to ream a naturalacetabulum in a patient, comprising the steps of: incising a hip with aminimally invasive incision; providing an acetabular reamer attachableto a driving tool, the reamer having a body that is adjustable to afirst position with a first shape that is a substantially hemisphericalshape and to a second position with a second shape that is substantiallysemicircular; positioning the reamer to the second position and secondshape; inserting the reamer through the minimally invasive incisionwhile in the second position; positioning the reamer from the secondposition to the first position and first shape; reaming the naturalacetabulum while the reamer is in the first position; positioning thereamer from the first position to the second position and second shape;removing the reamer from the minimally invasive incision while in thesecond position; and closing the incision.
 2. The method of claim 1,wherein the step of incising a hip creates the minimally invasiveincision with a length of about 2½ inches to about 4 to 5 inches.
 3. Themethod of claim 1, further comprising the step of providing the secondshape to be smaller than the first shape.
 4. The method of claim 3,further comprising the step of enlarging the reamer to perform the stepof positioning the reamer from the second position to the firstposition.
 5. The method of claim 3, further comprising the step ofreducing a size of the reamer to perform the step of positioning thereamer from the first position to the second position.
 6. The method ofclaim 1, further comprising the steps of collapsing the reamer toperform the step of positioning the reamer from the first position tothe second position, and expanding the reamer to perform the step ofpositioning the reamer from the second position to the first position.